1. Field of the Invention
This invention relates generally to traveling trolleys, and more particularly, to a single-rail trolley with a compact height.
2. Description of the Prior Art
A compact-height, travelling single rail trolley with a lifting mechanism or hoist is known from the published German Specification DE 42 09 565. In that publication, there is disclosed a trolley having wheels which run on the bottom flange of a rail and which are supported at a supporting frame. One of the wheels is driven and, rather than being connected directly with the supporting frame, is supported at a rocker which is arranged at the supporting frame so as to be pivotable. In addition, a friction wheel arranged at the rocker contacts the bottom flange of the rocker from below and forms a driving connection with the driven running wheel. The friction wheel and running wheel are arranged so as to be offset with respect to one another as seen in the traveling direction and can be adjusted at the bottom flange of the rail by swiveling the rocker so as to increase the frictional engagement. This swiveling movement is initiated on the one hand depending on load via the load acting on the supporting frame and, on the other hand, by a spring element arranged between the supporting frame and the rocker. Since the swiveling movement of the rocker causes a change in the position of the running wheel with respect to the bottom flange of the rail, the rocker is supported eccentrically. An adjustment of the eccentric changes the distance between the running wheel and the bottom flange and accordingly ensures that all running wheels are supported on the bottom flange.
Although this traveling trolley has proven advantageous in certain cases requiring great increases in frictional engagement, the arrangement of the supporting wheel and friction wheel at the rocker and the eccentric support of the latter at the supporting frame represents a costly solution when a substantial increase in frictional engagement is unnecessary.
In U.S. Pat. No. 2,617,365, it was proposed to provide a traveling trolley with a traveling mechanism or running gear for running on a rail and with a hoist arranged at the running gear. The running gear is connected via a tow bar with a driveable trolley unit provided with two running wheels which are movable on the bottom flange of the I-rail. Each running wheel is in a drive connection via toothed gears with a friction wheel which contacts the underside of the flange in the traveling direction so as to be slightly offset to the running wheels. The friction wheels are arranged on a shaft and driveable by a drive motor via a chain. The arrangement of the drive motor at a supporting plate in which the axle or shaft of the running wheel and friction wheel are fastened is effected in such a way that the inherent weight of the drive motor leads by way of the supporting plate acting as a lever to an increase in the contact pressure force of the running wheel and friction wheel against the bottom flange and accordingly to an increase in the frictional engagement.
A principal disadvantage of the configuration proposed in the aforementioned U.S. patent is that the connection of the running gear with the trolley unit via the tow bar results in a substantial increase in the constructional length of the traveling trolley. Moreover, although this type of construction guarantees an increase in the frictional engagement between the running wheel and friction wheel and the rail, this increase depends on the inherent weight of the drive motor and is very small. Further, this increase is not adjustable and does not allow for the different load situations of the traveling trolley.
A traveling trolley which carries a hoist and moves on the bottom flange of an I-rail by means of running wheels is proposed in German Patent DE-PS 1 259 070. The traveling trolley described therein is driven via a driven friction wheel which is pressed against the bottom flange from below. The contact pressure force can be applied and adjusted via a pretensioned spring. While this type of trolley drive is suitable in many cases owing to the adjustability of the contact pressure force of the friction wheel, the friction wheel must be manufactured from a rubber or plastic with good friction properties so as to transmit the requisite driving forces when the running wheels are not driven. This causes drive-related problems as a result of a decreased coefficient of friction due to moisture. Moreover, different loading states of the traveling trolley cannot be taken into account when adjusting the contact pressure force of the driven friction wheel.
A motor-driven traveling trolley with a non-driven counterwheel which is adjustable at the rail from below is proposed in German Patent Publication DE-PS 254 028. The counterwheel is arranged in a floating or oscillating manner at a supporting frame with running wheels, this arrangement being effected in such a way that a gap remains between the counterwheel and the rail when moving along horizontal portions of the rail and the counterwheel is pressed against the rail from below by means of the load acting indirectly thereon along ascending and descending stretches of the rail. Accordingly, a load-dependent increase in frictional engagement is effected between the wheels and the rail. Motor-driven trolleys of this kind enable a load-dependent increase in frictional engagement along ascending and descending lengths of the rail, but not along horizontal portions which are commonly used in traveling trolleys with hoists.
Another type of bottom-flange traveling trolley of compact height is also known from DE-PS 491 527. This traveling trolley substantially has a hoist, a supporting frame, a running gear with a drive mechanism, and a counterweight. The hoist and the drive mechanism are attached to opposite sides of the supporting frame engaging at the bottom of an I-shaped travel rail at roughly the same height as the rail. On the side of the supporting frame opposite the hoist, a counterweight is arranged in order to balance the traveling trolley in such a way that the center of gravity lies under the center of the rail. Although this short traveling trolley has a compact height, a counterweight is needed to balance the trolley due to the eccentric arrangement of the hoist. Accordingly, in addition to a disadvantageous increase in the inherent weight, the size of the traveling trolley is usually also increased, in particular when the counterweight is fastened at the supporting frame via lever arms.
It is therefore an object of the present invention to provide a single-rail trolley which has a low overall height, which is compact and simple to manufacture, and which includes a reliable drive.